PHELAN — The source of what caused dozens of horses in the High Desert to become ill may have spread to another county.

After horses in the Phelan area began experiencing mysterious swollen eyes and lips, blisters on their muzzles and a loss of hair, as many as seven cases were reported in the Riverside County city of Norco.

According to a report in the Riverside Press-Enterprise on Wednesday, the affected horses experience infections called photodermatitis, which can result in hair loss and painful lesions.

State officials said tainted hay is suspected of causing sun sensitivity that is leading to rashes and skin infections in the horses, with the source appearing to be tainted alfalfa hay.

The feed seems to have originated from several distributors, with at least some from the Bishop area in the Eastern Sierra, according to the California Department of Food and Agriculture’s Animal Health and Food Safety Services Division.

Toxicologists have not definitively identified the exact substance, but officials believe it might be naturally occurring, the agency’s Dr. Kent Fowler said.

A lack of water caused by California’s severe drought might have caused the levels of some ingredients in alfalfa hay to change, officials said. The problem could stem from the hay being fed to horses very soon after it was cut and baled. The effect might lessen over time in hay that is kept awhile, the Press-Enterprise reported.

Many Phelan horse owners also speculated that the drought or high levels of protein in the hay may have caused their horse to become ill.

State officials said the condition is typically not fatal, unless a secondary condition, such as an infection, gets out of control. A horse owner in the Phelan area reported two old horses died of what she believed was photosensitization in recent months, but an investigation didn’t find that sun sensitivity was involved, Fowler said.

Veterinarians said treatment starts with getting horses under shelter or shade, and sometimes turning them out only at night. They should be kept out of sunlight until they heal. Open sores resulting from severe cases might get bacterial infections, which would then most likely require antibiotics administered by a vet.

“My horse, Sandy, is getting better by the day,” said Julie Gioventi, of Phelan. “Plenty of water, shade, fresh feed and rest cleared up her blisters in no time.”

Locally, the medical condition may have been brought on by feed that was sold at Diamond B Hay and Feed at the end of July, and was “isolated to one load of alfalfa, just at the Phelan location,” said Chuck Burt of Diamond B Hay and Feed.

Burt said the University of California, Davis tested the hay, which came back clean. The university said the sickness could be an anomaly that was caused by the drought, he said.

Several factors can make the skin sensitive to UV rays, including having an inherited tendency to photosensitivity, taking certain medications, or being exposed to certain plants.

Burt said there is speculation that the sickness could be a virus, and that a similar outbreak has been reported in Texas and Colorado.

After the Daily Press story about the sick Phelan horses ran in early August, equine owners from North Carolina, Northern California, Oklahoma and Arizona, called the paper and commented that their horses were also experiencing similar symptoms.